Insulated Pedicle Access System and Related Methods

ABSTRACT

A pedicle access system including a cannula, a stylet, and a removable T-handle. The pedicle access system may be used to percutaneously approach the pedicle, initiate pilot hole formation, and conduct a stimulation signal to the target site for the purposes of performing a pedicle integrity assessment during the pilot hole formation. To do this, the cannula and stylet are locked in combination and inserted through an operating corridor to the pedicle target site, using the T-handle to facilitate easy movement and positioning of the cannula/stylet combination. A stimulation signal may be applied during pilot hole formation to conduct the pedicle integrity assessment. In a significant aspect, the T-handle may be detached from the cannula/stylet combination to facilitate the use of various surgical tools as necessary.

CROSS-REFERENCES TO RELATED APPLICATIONS

The present application is a continuation of U.S. patent applicationSer. No. 14/338,154, filed Jul. 22, 2014, which is a continuation ofU.S. patent application Ser. No. 13/109,981, filed May 17, 2011, nowissued as U.S. Pat. No. 8,784,330 (the contents being incorporatedherein by reference), which is a continuation of U.S. patent applicationSer. No. 11/448,237, filed Jun. 6, 2006, now issued as U.S. Pat. No.7,942,826 (the contents being incorporated by reference), which claimspriority from U.S. Provisional Patent Application Ser. No. 60/687,947,filed Jun. 6, 2005 (the contents being incorporated herein byreference).

BACKGROUND OF THE INVENTION I. Field of the Invention

The present invention relates to a system and methods aimed at accessinga pedicle in preparation for the placement of pedicle screws.

II. Discussion of the Prior Art

An emerging trend in spinal surgery is to perform surgery in a minimallyinvasive or minimal access fashion to avoid the trauma of so-called openor “direct access” procedures. A specific area of interest is in theplacement of pedicle screws, which are typically employed to effectposterior fixation in spinal fusion procedures. While great strides arebeing made in this area, a risk exists (as it does in open procedures)that the pedicle may become breached, cracked, or otherwise compromisedduring the procedure. If the pedicle (or more specifically, the cortexof the medial wall, lateral wall, superior wall and/or inferior wall) isbreached, cracked, or otherwise compromised, the patient may experiencepain or neurologic deficit due to unwanted contact between the pediclescrew and exiting nerve roots. This often necessitates revision surgery,which can be painful and costly, both in terms of recovery time andhospitalization.

Some attempts to minimize the risk of a pedicle breach involvecapitalizing on the insulating characteristics of bone and theconductivity of the exiting nerve roots themselves to perform pedicleintegrity assessments. That is, if the wall of the pedicle is breached,a stimulation signal applied to the pedicle screw and/or the pilot hole(prior to screw introduction) will cause the various muscle groupscoupled to the exiting nerve roots to contract. If the pedicle wall hasnot been breached, the insulating nature of the pedicle will prevent thestimulation signal from innervating the given nerve roots such that theassociated muscle groups will not twitch. Traditional EMG monitoringsystems may be employed to augment the ability to detect suchinnervation.

One period during a pedicle screw procedure in which the risk of apedicle breach is prevalent is during the initial access of the pedicle.Typically, initial access to a pedicle may be achieved by inserting aneedle to the target site and driving the needle point into the pedicle,creating a pilot hole. Due to the size and shape of the typical needle,however, manipulation and maneuvering of the needle may be awkward ordifficult, increasing the risk of complication. Additionally, thepedicle may be breached and nerve damage done during the initial driveof the needle into the pedicle, before a pedicle integrity testassessment may be performed.

A problem that may arise when various medical instruments areelectrified and used with traditional EMG monitoring systems is thatdifferent instruments may produce different EMG stimulation thresholds.For example, an electrified needle may exhibit a threshold stimulationof approximately 5-6 mA, while a bone screw placed in the same locationmay exhibit a threshold stimulation of approximately 16-20 mA. This canbe problematic in that an electrified needle may tend to indicate abreach in the pedicle wall when in fact the pedicle wall is intact.

The present invention is directed at eliminating, or at least improvingupon, the shortcomings of the prior art.

SUMMARY OF THE INVENTION

The present invention provides a pedicle access system that facilitatesease of handling and can achieve dynamic pedicle integrity testing whileforming a pilot hole.

According to a broad aspect of the present invention the pedicle accesssystem includes a cannula, a stylet, and a removable T-handle. Thepedicle access system of the present invention may be used topercutaneously approach the pedicle, initiate pilot hole formation, andconduct a stimulation signal to the target site for the purposes ofperforming a pedicle integrity assessment during the pilot holeformation. To do this, the cannula and stylet are locked in combinationand inserted through an operating corridor to the pedicle target site,using the T-handle to facilitate easy movement and positioning of thecannula/stylet combination. A stimulation signal may be applied duringpilot hole formation to conduct the pedicle integrity assessment. In asignificant aspect of the present invention, the T-handle may bedetached from the cannula /stylet combination to facilitate the use ofvarious surgical tools as necessary.

The cannula includes a coupling element and an elongated shaft. Aninterior lumen extends through the cannula from a first opening in thecoupling element to a second opening in the distal region of theelongated shaft. The elongated shaft may be composed of a conductivematerial, such as metal. A polymeric coating blankets or otherwiseencapsulates a majority of the exterior surface of the elongated shaft,such that the elongated shaft includes an insulated region and anuninsulated region. The elongated shaft may incorporate one or morediameter changes along its length.

The coupling element comprises three sections. First, a proximal regionis dimensioned to engage with the stylet. The proximal region may alsoinclude at least one tab member protruding in a generally lateraldirection. The tab member functions to lock the cannula and stylet inposition together. Second, a center section is dimensioned to engagewith the T-handle. At least one cutout may be provided in the exteriorsurface of the center section. The cutout functions to secure theT-handle to the cannula/stylet combination, or optionally to the cannulaonly. Finally, there is a base portion having a circumference greaterthan that of the center section such that a ledge is formed at theinterface of the center section and the base portion.

The stylet comprises a locking cap and a needle element. The locking caphas a similar size and shape as the center section. The locking capcontains a generally cylindrical aperture dimensioned to receive thegenerally cylindrical top section of the cannula. Furthermore, thelocking cap includes at least one longitudinal channel and at least onelateral channel that interact with the tab member as a means to securethe stylet and cannula in place.

The longitudinal channel has a length dimension corresponding to thelength of the generally cylindrical aperture and a width dimensionsufficient to accommodate the length of the tab member. The lateralchannel extends generally perpendicularly from the proximal end of thelongitudinal channel, such that together the channels form a generallyhalf-T shape. The longitudinal channel and the lateral channel, alongwith a ridge positioned on at least one edge of the lateral channelinteract with the tab member on the cannula to lock the stylet andcannula together. Additionally, the locking cap may include a rampedsurface to facilitate engagement with the T-handle.

The proximal portion of the needle element may be attached to theinterior of the locking cap. The elongated shaft of the needle elementextends distally from the proximal portion, with a significant portionprotruding from the opening of the generally cylindrical aperture. Theneedle element is dimensioned to be inserted through the interior lumenof the cannula. When fully inserted, a distal portion of the needleelement may protrude slightly from the bottom opening of the cannula.The needle element may be composed of a conductive material, such asmetal, or a non-conductive material with one or more embedded conductiveelements at or near the distal end capable of being communicativelylinked with a pedicle integrity testing system.

To combine the cannula and stylet, the needle element is inserted intothe interior lumen of the cannula through the opening in the couplingelement. The locking cap is positioned such that its longitudinalchannels are aligned with the tab members of the cannula. The proximalregion of the cannula is received into the aperture on the locking cap,and the tab members pass through the longitudinal channels. Insertion iscomplete when the proximal region is fully received by the aperture,leaving the locking cap in an “unlocked” position. In the unlockedposition, the tab members are positioned at the proximal ends of thelongitudinal channels. In this position the locking cap and centersection of the cannula are not aligned. To lock the stylet in place inthe cannula, the locking cap is rotated until it is aligned with thecenter section. As the lateral channels rotate around the tab members,the ridges may be deformed when they contact the tab members. When thelocking cap and center section align, the ridges may clear the tabmembers and regain their original forms, thereby preventing inadvertentrotation back to the unlocked position.

The T-handle includes a grip region, an aperture for engaging thecannula or cannula/stylet combination, and a locking mechanism forsecuring the T-handle to the cannula. The T-handle aperture isdimensioned to snugly receive both the locking cap and the centersection of the cannula when they are aligned in the locked position. Thelocking mechanism preferably comprises a lever having one end integratedinto the aperture wall and a free end extending therefrom. The majorityof the lever (excluding the free end) may be the same thickness as theaperture wall and does not protrude, interiorly or exteriorly, from theaperture wall. In its “natural” state, the free end does protrude intothe aperture space. The free end is dimensioned to engage the cutout inthe center section of the cannula. The interior surface of the free endmay be slightly ramped. The ramped portion works in concert with theramped surface of the locking cap to force the free end out of itsnatural state so the locking cap and the center section can fit into theT-handle aperture. When the locking cap and center section are fullyinserted into the T-handle aperture, the locking mechanism aligns withthe cutout in the cannula, returns to its natural state, and locks theT-handle to the cannula. Optionally, the T-handle may be cannulated.

In an alternative aspect of the present invention, the pedicle accesssystem may be provided with a stylet, a cannula and a lock collar. Anypart of the stylet and/or cannula may be coated with a nonconductiveinsulative coating to prevent shunting of electrical current.

In a further alternative aspect of the present invention, the pedicleaccess system may be provided with a retractable insulation sheathdimensioned to cover the electrically conductive cannula and styletneedle. The retractable insulation sheath is adapted to electricallyinsulate the pedicle access system as it is advanced along an operativecorridor to a bony structure. As the needle element is introduced intothe bony structure (e.g. a pedicle) during pilot hole formation, theinsulation sheath retracts to remain outside the bone and preventelectrical current intended for the pilot hole from shunting tosurrounding tissue.

In a significant aspect of the present invention, the pedicle accesssystem may be used in combination with neurophysiology monitoringsystems and methods to conduct pedicle integrity assessments whileachieving initial access to the pedicle and forming a pilot hole. Theneurophysiology system performs pedicle integrity assessments bydetermining the amount of electrical communication between a stimulationsignal and the adjacent nerve root. The pedicle access system may becoupled with the neurophysiology system by attaching an electriccoupling device to the uninsulated region of the cannula.

In another significant aspect of the present invention, the pedicleaccess system may be used in cooperation with spinal fixation systemsthat require access to pedicle target sites and need pilot holes, as thecannula may be used to guide parts of the surgical fixation system tothe target site.

BRIEF DESCRIPTION OF THE DRAWINGS

Many advantages of the present invention will be apparent to thoseskilled in the art with a reading of this specification in conjunctionwith the attached drawings, wherein like reference numerals are appliedto like elements and wherein:

FIG. 1 is a plan view of an example of a pedicle access system accordingto one embodiment of the present invention;

FIG. 2 is a perspective view of a cannula forming part of the pedicleaccess system of FIG. 1;

FIG. 3 is a perspective view of a coupling element forming part of thecannula of FIG. 2;

FIG. 4 is a perspective view of a stylet forming part of the pedicleaccess system of FIG. 1;

FIG. 5 is a perspective view of a locking cap forming part of the styletof FIG. 4;

FIG. 6 is a perspective view of the distal portion of the stylet of FIG.4 protruding from the distal region of the cannula of FIG. 2;

FIG. 7 is a perspective view of the distal portion of the stylet of FIG.4 protruding from the distal region of the cannula of FIG. 2, with thedistal region of the cannula having an uninsulated portion;

FIG. 8 is a perspective view of the distal portion of the stylet of FIG.4 protruding from the distal region of the cannula of FIG. 2, with thedistal region of the cannula having a directional electrode;

FIGS. 9-10 are plan and perspective views, respectively, of the styletof FIG. 4 partially inserted into the cannula of FIG. 2;

FIG. 11 is a is a plan view of the stylet of FIG. 4 fully inserted intothe cannula of FIG. 2 in an unlocked position;

FIG. 12 is perspective view of the locking cap of the fully insertedstylet of FIG. 11, shown in an unlocked position;

FIG. 13 is a perspective view of the cannula and stylet combination inthe unlocked position of FIG. 11;

FIGS. 14-15 are perspective and plan views, respectively, of the cannulaand stylet combination of FIG. 13 in the locked position;

FIGS. 16-17 are perspective views of a T-handle forming part of thepedicle access system of FIG. 1;

FIG. 18 is a perspective view of the pedicle access system of FIG. 1with the cannula and stylet combination of FIG. 13 fully inserted andlocked in the T-handle;

FIG. 19 is an exploded perspective view of a pedicle access systemaccording to an alternative embodiment of the present invention;

FIG. 20 is a perspective view of the assembled pedicle access system ofFIG. 19;

FIGS. 21-22 are plan and perspective views, respectively, of a cannulaforming part of the pedicle access system of FIG. 20;

FIGS. 23-24 are plan and perspective views, respectively, of a couplingelement forming part of the cannula of FIG. 21;

FIG. 25 is a perspective view of a stylet forming part of the pedicleaccess system of FIG. 20;

FIG. 26 is a perspective view of a handle forming part of the stylet ofFIG. 25;

FIG. 27 is a perspective view of the pedicle access system of FIG. 20including an enlarged view of a distal region thereof;

FIGS. 28-30 are perspective, top plan and bottom plan views,respectively, of a lock collar forming part of the pedicle access systemof FIG. 20;

FIG. 31 is an exploded perspective view of a pedicle access systemaccording to a further alternative embodiment of the present invention;

FIGS. 32-33 are perspective views of an assembled pedicle access systemof FIG. 31;

FIG. 34 is a front view of the pedicle access system of FIG. 32;

FIGS. 35-36 are side and perspective views, respectively, of a cannulaforming part of the pedicle access system of FIG. 31;

FIGS. 37-38 are side and perspective views, respectively, of a couplingelement forming part of the cannula of FIG. 35;

FIG. 39 is a perspective view of a stylet forming part of the pedicleaccess system of FIG. 31;

FIG. 40 is a perspective view of a needle forming part of the stylet ofFIG. 39;

FIGS. 41-42 are perspective and plan views, respectively, of a handleforming part of the stylet of FIG. 39;

FIGS. 43-44 are perspective and plan views, respectively, of a lockcollar forming part of the pedicle access system of FIG. 31;

FIG. 45 is a bottom plan view of a handle of FIG. 46 in engagement witha lock collar of FIG. 43;

FIG. 46 is a perspective view of a retractable insulation sheath formingpart of the pedicle access system of FIG. 31;

FIG. 47 is a perspective view of an insulation tube forming part of theretractable insulation sheath of FIG. 46;

FIG. 48 is a perspective view of a retraction tube forming part of theretractable insulation sheath of FIG. 46;

FIGS. 49-50 are perspective views of a sheath attachment element formingpart of the pedicle access system of FIG. 31; and

FIG. 51 is a perspective view of an example of a neurophysiology systemcapable of connecting to the pedicle access systems of FIGS. 1, 19 and31 to conduct pedicle integrity tests.

FIGS. 52-53 are side and perspective views, respectively, of a cannulaforming part of the pedicle access system of FIG. 51;

FIG. 53A are cross-sectional views taken along lines 53A-53A in FIG. 53illustrating the relative size of the insulated and non-insulatedregions of the cannula of FIGS. 51-53; and

FIG. 54 is a perspective view of an example of a neurophysiology systemcapable of connecting to the pedicle access systems of FIGS. 1, 19, and31 to conduct pedicle integrity tests.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Illustrative embodiments of the invention are described below. In theinterest of clarity, not all features of an actual implementation aredescribed in this specification. It will of course be appreciated thatin the development of any such actual embodiment, numerousimplementation-specific decisions must be made to achieve thedevelopers' specific goals, such as compliance with system-related andbusiness-related constraints, which will vary from one implementation toanother. Moreover, it will be appreciated that such a development effortmight be complex and time-consuming, but would nevertheless be a routineundertaking for those of ordinary skill in the art having the benefit ofthis disclosure. The insulated pedicle access system and related methodsdisclosed herein boast a variety of inventive features and componentsthat warrant patent protection, both individually and in combination.

FIG. 1 illustrates an example of a pedicle access system 10 according toone embodiment of the present invention. The pedicle access system 10includes a cannula 12, a stylet 14, and a T-handle 16. As will bedescribed with greater detail below, the pedicle access system 10 may beused to percutaneously approach the pedicle, initiate pilot holeformation, and conduct a stimulation signal to the target site for thepurposes of performing a pedicle integrity assessment during formationof the pilot hole. To do this, the cannula 12 and stylet 14 may belockingly mated to form a cannula/stylet combination 15 which may beinserted through an operating corridor to the pedicle target site, usingthe T-handle 16 to facilitate easy movement and positioning of thecannula/stylet combination 15. The cannula/stylet combination 15 may bedriven into the bone at the target site to form a pilot hole while astimulation signal is applied to the pedicle access system 10 andconducted to the target site to assess the integrity of the pedicleduring hole formation. The T-handle 16 may be detached from thecannula/stylet combination 15 to facilitate the use of various surgicaltools (such as by way of example only a forceps, mallet, or needledriver) after proper positioning of the cannula 12 and stylet 14.Additionally, removal of the T-handle after proper positioning of thecannula/stylet combination 15 provides a less obstructed view of theoperating corridor and surgical target site. As shown and describedherein, the cannula 12 and stylet 14 are generally cylindrical in shape.However, it should be understood that cannula 12 and stylet 14 may beprovided in any suitable shape having any suitable cross-section (e.g.generally oval or polygonal) without deviating from the scope of thepresent invention.

FIG. 2 illustrates an example of a cannula 12 forming part of pedicleaccess system 10. Cannula 12 includes a coupling element 18 and anelongated shaft 20. An interior lumen extends through the cannula 12from a first opening 22 located at a proximal region 30 of the couplingelement 18 to a second opening 24 located at a distal end 21 of theelongated shaft 20. Elongated shaft 20 may be composed of any conductivematerial such as metal, for example. A polymeric coating is provided ona substantial portion of the exterior surface of elongated shaft 20 suchthat elongated shaft 20 comprises an insulated portion 26 and anuninsulated portion 28. Although elongated shaft 20 is shown having asingle uniform diameter, it will be appreciated that one or morediameter changes may be incorporated along the elongated shaft 20without deviating from the scope of the present invention.

With reference to FIG. 3, coupling element 18 comprises a proximalregion 30, a center section 32, and a base portion 34. Proximal region30 is dimensioned to engage with the stylet 14 (described below).Proximal region 30 may include at least one tab member 36 that protrudesin a generally lateral direction from the proximal region 30. By way ofexample only, as shown in FIG. 3 proximal region 30 includes two tabmembers 36 positioned opposite one another and adjacent to first opening22. As will be described in greater detail below, tab members 36function to lock the cannula 12 and stylet 14 together. Center section32 is dimensioned to be received within T-handle aperture 66 (FIG. 16)as described in further detail below. Center section 32 may be providedwith at least one cutout 38 dimensioned to receive a locking mechanism68 (FIG. 16) incorporated into T-handle 16 to secure the T-handle 16 tothe cannula/stylet combination 15, or optionally to the cannula 12 only.The base 34 has a circumference that is greater than the circumferenceof center section 32, such that a ledge 39 is formed at the interface ofcenter section 32 and the base portion 34. The ledge 39 engages the rim72 of T-handle 16 so as to minimize potential stress on a T-handlelocking mechanism 68 discussed below.

FIG. 4 illustrates an example of a stylet 14 forming part of the pedicleaccess system 10. Stylet 14 includes a locking cap 40 and a needleelement 42. Locking cap 40 has a similar size and shape to centersection 32, and is similarly dimensioned to be received within T-handleaperture 66, discussed below. Locking cap 40 includes a distal end 44and a proximal end 46. As illustrated in FIG. 5, locking cap 40 includesa generally cylindrical aperture 48 having an opening at distal end 44and extending in a proximal direction at least partially the length oflocking cap 40. Generally cylindrical aperture 48 is dimensioned toreceive the generally cylindrical proximal region 30 of cannula 12.Furthermore, locking cap 40 includes at least one longitudinal channel50 (defined by an axis extending through the proximal and distal ends46, 44 respectively) and at least one lateral channel 52 extendinggenerally perpendicularly from longitudinal channel 50. Longitudinalchannel 50 and lateral channel 52 each extend from an exterior surface54 through an interior surface 56 into aperture 48. Preferably, thenumber of longitudinal channels 50 and lateral channels 52 correspond tothe number of tab members 36 on cannula 12. By way of example only (andas shown in FIGS. 3-5), cannula 12 includes two tab members 36 andstylet 14 includes two longitudinal channels 50 and two lateral channels52.

Longitudinal channel 50 initiates at the distal end 46 and has a lengthcorresponding to the length of the generally cylindrical 48. Lateralchannel 52 initiates at the proximal end of longitudinal channel 50 andextends generally perpendicularly therefrom such that together thelongitudinal and lateral channels 50, 52 form a generally half-T shape.Longitudinal channel 50 and lateral channel 52 function to interact withthe tab 36 on cannula 12, so as to lock the stylet 14 and cannula 12together. Longitudinal channel 50 has a width dimension sufficient toaccommodate the length of tab member 36 and lateral channel 52 has aheight dimension sufficient to accommodate the height of tab member 36(best viewed in FIG. 12). A ridge 58 (shown in FIG. 12) may bepositioned along the distal-most edge 53 and/or proximal-most edge 55 ofthe lateral channel 52 to engage with tab member 36 and provide alocking means for the cannula/stylet combination 15. Additionally, aportion of exterior surface 54 adjacent to proximal end 46 may comprisea ramped surface 49 such that the circumference of distal end 44 isslightly greater than the circumference of proximal end 46, so as tofacilitate engagement with the T-handle 16.

The needle element 42 comprises an elongated shaft 41 having a proximalregion 43 and a distal region 45. The proximal region 43 may be attachedto the interior of locking cap 40 between proximal end 46 and aperture48. Elongated shaft 41 extends distally from proximal region 43 with asignificant portion protruding generally perpendicularly from theopening of aperture 48. Needle element 42 is dimensioned to be insertedthrough the interior lumen of cannula 12. The distal region 45 generallyincludes a distal portion of elongated shaft 41 and a shaped tip 47having any form or shape capable of being driven into the pedicle tocreate a pilot hole. By way of example only, shaped tip 47 may have abeveled or double diamond form. As illustrated in FIG. 6, when needleelement 42 is fully inserted into cannula 12, at least a portion ofdistal region 45 (including shaped tip 47) may protrude slightly fromthe second opening 24 of cannula 12. Due to the insulated nature ofcannula 12, the portion of needle element 42 that protrudes from cannula12 effectively constitutes a stimulation region 60. The stimulationregion 60 may include the distal region 45 and/or the shaped tip 47.

According to a further aspect of the present invention, any part of theneedle element 42 (e.g. the elongated shaft 41, distal region 45 and/orshaped tip 47) may be provided with a coating to insulate and thereforelimit or reduce the stimulation region 60 to a desired configuration.For example, the distal tip 47 may have an insulation coating toeffectuate a stimulation region 60 consisting of the portion of thedistal region 45 of the needle element 42 between the insulated cannula12 and the insulated distal tip 47. Alternatively, the entirety ofneedle element 42 may be provided with an insulative coating and thedistal region 21 of cannula 12 may be provided with (for example) one ormore uninsulated portions 29 (FIG. 7) and/or one or more directionalelectrodes 31 (FIG. 8) forming a stimulation region 61. Thesealternative arrangements serve to mitigate an apparent phenomenon inwhich certain geometries (e.g. points and edges) tend to generatesignificantly higher current densities and therefore are much moreefficient at exciting a nearby nerve, even through bone tissue. As aresult, instrumentation having these geometries may show a lowerstimulation threshold (and thus causing an EMG monitoring system toindicate a breach in an intact pedicle) unless this phenomenon isotherwise compensated for.

Needle element 42 may be composed of a conductive material, such asmetal. Alternatively, needle element 42 may be composed of anon-conductive material with one or more embedded conductive elements ator near the distal end (e.g. distal region 45 and/or shaped tip 47)capable of being communicatively linked with a pedicle integrity testingsystem.

FIGS. 9-15 illustrate the formation of the cannula/stylet combination15. In FIGS. 9-10 stylet 14 is introduced into cannula 12. Needleelement 42 of stylet 14 is inserted into the interior lumen of cannula12 through the first opening 22 of coupling element 18. The locking cap40 of stylet 14 is positioned such that its longitudinal channels 50 arealigned with the tab members 36 of cannula 12. The proximal region 30 ofcannula 12 is received into the aperture 48 of locking cap 40, and thetab members 36 pass through the longitudinal channels 50 as insertion ofneedle element 42 progresses. Insertion is complete when the proximalportion 30 is fully received by aperture 48, leaving the locking cap 40in the “unlocked” position illustrated in FIGS. 11-13. As mentionedabove, the distal region 45 of needle element 42 including shaped tip 47(and the stimulation region 60) may protrude from the second opening 24of the elongated shaft 20 of cannula 12 when stylet 14 is fullyinserted, shown in FIG. 11. In the unlocked position, tab members 36 arepositioned at the proximal end of longitudinal channels 50 where thechannels intersect lateral channels 52. At this point, the correspondingshapes of the locking cap 40 of stylet 14 and center section 32 ofcannula 12 are out of alignment. To lock stylet 14 in place and completethe combination, the locking cap 40 is rotated until it is aligned withthe center section 32 as illustrated in FIGS. 14-15. As the lateralchannels 52 rotate around the tab members 36, ridges 58 come intocontact with the tab members 36. The ridges may not pass the tab members36 if the locking cap 40 is not rotated with enough force to deform theridges 58. Once the ridges 58 have deformed, the rotation may continuetowards the final position. The locking cap 40 and center section 32become aligned and the ridges 58 may clear the tab members 36 and regaintheir original forms, thereby preventing inadvertent rotation of thelocking cap 40 back to the unlocked position.

FIG. 16 illustrates an example of a T-handle 16 forming part of thepedicle access system 10. T-handle 16 includes a grip region 64, anaperture 66 for engaging the cannula 12 or cannula/stylet combination15, and a locking mechanism 68 for securing the T-handle to the cannula12. Grip region 64 may be provided in any number of suitable shapes andsizes that may aid the user in holding and manipulating the pedicleaccess system 10 during use. The T-handle aperture 66 is dimensioned tosnugly receive both the locking cap 40 and center section 32 when theyare aligned in the locked position as described above. The lockingmechanism 68 preferably comprises a lever having one end that isintegrated into the aperture wall and a free end 70 extending therefrom.The majority of the locking mechanism 68 (excluding free end 70) maycomprise the same thickness as the aperture wall and does not protrude,interiorly or exteriorly, from the aperture wall. In its “natural”state, the interior surface of free end 70 protrudes into the aperture66 space. The interior surface of free end 70 is dimensioned to engagethe cutout 38 in the center section 32 of cannula 12. Furthermore, asillustrated in FIG. 17, the interior surface of free end 70 may beslightly ramped, such that the edge further from the aperture openingprotrudes further into the aperture than the edge closer to the apertureopening. The ramped portion works in concert with the ramped surface 49at the proximal end 46 of locking cap 40 to force the free end 70 out ofits natural state as the locking cap 40 of stylet 14 and center section32 of cannula 12 are received into the T-handle aperture 66. When thelocking cap 40 and center section 32 are fully inserted into theT-handle aperture 66, as illustrated in FIG. 18, the interior surface offree end 70 aligns with the cutout 38 in the center section 32 and freeend 70 returns to its natural state, thus locking the T-handle 16 to thecannula 12. Furthermore, as the locking cap 40 and center section 32 arefully inserted into the T-handle aperture 66, the ledge 39 engages therim 72. This interaction functions to minimize potential stress on theT-handle locking mechanism 68 by increasing the surface area thatreceives force applied by the user. To remove the T-handle 16, the freeend 70 may be lifted to disengage with the cutout 38, and the T-handlemay be pulled off. Optionally, T-handle 16 may be cannulated (not shown)such that an interior lumen extends from an opening on the top of thehandle into the aperture 66.

FIGS. 19-20 illustrate an example of a pedicle access system 110according to an alternative embodiment of the present invention. Thepedicle access system 110 includes a cannula 112, a stylet 114, and alock collar 116. As described above in relation to pedicle access system10, pedicle access system 110 may be used to percutaneously approach thepedicle, initiate pilot hole formation, and conduct a stimulation signalto the target site for the purposes of performing a pedicle integrityassessment during formation of the pilot hole. To do this, the cannula112 and stylet 114 may be lockingly mated and inserted through anoperating corridor to the pedicle target site, using the handle portion140 of the stylet 114 to facilitate easy movement and positioning ofpedicle access system 110. The pedicle access system 110 may be driveninto the bone at the target site to form a pilot hole while astimulation signal is applied and conducted to the target site to assessthe integrity of the pedicle during hole formation. As shown anddescribed herein, the cannula 112 and stylet 114 are generallycylindrical in shape. However, it should be understood that cannula 112and stylet 114 may be provided in any suitable shape having any suitablecross-section (e.g. generally oval or polygonal) without deviating fromthe scope of the present invention.

FIGS. 21-22 illustrate an example of a cannula 112 forming part ofpedicle access system 110. Cannula 112 includes a coupling element 118and an elongated shaft 120. An interior lumen extends through thecannula 112 from a first opening 122 located at a proximal region 130 ofthe coupling element 118 to a second opening 124 located at a distal end121 of the elongated shaft 120. Elongated shaft 120 may be composed ofany conductive material such as metal, for example. A polymeric coatingmay be provided on a substantial portion of the exterior surface ofelongated shaft 120 such that elongated shaft 120 comprises an insulatedportion 126 and an uninsulated portion 128 (the edge of the coating andthus the boundary between portions 126, 128 represented by callout 127in FIGS. 21-22). Elongated shaft 120 may include any number of diameterchanges incorporated along its length without deviating from the scopeof the present invention. In the alternative, elongated shaft 120 may beprovided with a uniform diameter along its length.

With reference to FIGS. 23-24, coupling element 118 comprises a proximalregion 130, a center section 132, and a distal portion 134. Proximalregion 130 includes an engagement region 131 dimensioned to engage withthe handle portion 140 of the stylet 114 (as described in further detailbelow). The engagement region 121 may be provided in any suitablegeometric configuration to allow for secure mating with the engagementtabs 144 of the handle 140. By way of example only, the coupling element118 is shown in FIGS. 23-24 having a hexagonal engagement region 131,however other shapes are possible. Proximal region 130 may include atleast one tab member 136 that protrudes in a generally lateral directionfrom the proximal region 130. By way of example only, as shown in FIG.24 proximal region 130 includes two tab members 136 positioned oppositeone another and adjacent to first opening 122. Tab members 136 may beutilized to attach supplemental instruments and/or apparatuses to thecannula 112. Center section 132 may be provided with a diameter that islarger than the diameters of the proximal region 130 and distal portion134, and may be provided with a plurality of ridges 133 and/or otherfeatures for the purpose of providing a suitable gripping area for auser. The distal portion 134 is dimensioned to engage with the elongatedshaft 120 of the cannula 112.

FIG. 25 illustrates an example of a stylet 114 forming part of thepedicle access system 110. Stylet 114 includes a handle portion 140 anda needle element 142. Handle portion 140 may (by way of example)resemble a T-handle for providing a user with a suitable gripping means.Handle portion 140 may be provided with a pair of engagement tabs 144extending distally from handle portion 140. Engagement tabs 144 extendgenerally perpendicularly from the handle 140 and generally parallel toone another such that the engagement tabs 144 collectively faun aninterior space 146. Interior space 146 is dimensioned to receive theproximal region 130 of the coupling element 118 of the cannula 112. Eachengagement tab 144 is provided with a medial (inwardly-facing)indentation 148 and a lateral (outwardly-facing) indentation 150. Medialindentations 148 are dimensioned to engage the engagement region 131 ofthe coupling element 118, described above. For this reason, the medialindentations 148 may be provided with any geometry complementary to theshape of the engagement region 131 such that when mated, the engagementtabs 144 (via the medial indentations 148) will prevent movement of theengagement region 131, in effect locking the cannula 112 in placerelative to the stylet 114. The lateral indentations 150 are dimensionedto interact with the first and second protrusions 170, 172 of the lockcollar 116 described in further detail below.

The needle element 142 comprises an elongated shaft 152 having aproximal region 154 and a distal region 156. The proximal region 154 maybe attached to the interior of handle portion 140. Elongated shaft 152extends distally from proximal region 154 and generally perpendicularlyfrom the handle 140. Needle element 142 is dimensioned to be insertedthrough the interior lumen of cannula 112. The distal region 156generally includes a distal portion of elongated shaft 152 and a shapedtip 158 having any form or shape capable of being driven into thepedicle to create a pilot hole. By way of example only, shaped tip 158may have a beveled or double diamond form. As illustrated in FIG. 27,when needle element 142 is fully inserted into cannula 112, at least aportion of distal region 156 (including shaped tip 158) may protrudeslightly from the second opening 124 of cannula 112. Due to theinsulated nature of cannula 112, the portion of needle element 142 thatprotrudes from cannula 112 effectively constitutes a stimulation region160. The stimulation region 160 may include the distal region 152 and/orthe shaped tip 158.

According to a further aspect of the present invention, any part of theneedle element 142 (e.g. the elongated shaft 152, distal region 156and/or shaped tip 158) may be provided with a coating to insulate andtherefore limit or reduce the stimulation region 160 to a desiredconfiguration. For example, the distal tip 158 may have an insulationcoating to effectuate a stimulation region 160 consisting of the portionof the distal region 156 of the needle element 142 between the insulatedcannula 112 and the insulated distal tip 158. This coating serves tomitigate an apparent phenomenon in which certain geometries (e.g. pointsand edges) tend to generate significantly higher current densities andtherefore are much more efficient at exciting a nearby nerve, eventhrough bone tissue. As a result, instrumentation having thesegeometries may show a lower stimulation threshold (and thus causing anEMG monitoring system to indicate a breach in an intact pedicle) unlessthis phenomenon is otherwise compensated for.

Needle element 142 may be composed of any conductive material, such asmetal. Alternatively, needle element 142 may be composed of anon-conductive material with one or more embedded conductive elements ator near the distal end (e.g. distal region 156 and/or shaped tip 158)capable of being communicatively linked with a pedicle integrity testingsystem.

With reference to FIGS. 28-30, a lock collar 116 is provided tolockingly mate the cannula 112 and the stylet 114. Lock collar 116 has agenerally cylindrical overall shape, and includes a proximal portion162, a distal portion 164 and an interior lumen 166 extendingtherethrough. The proximal portion 162 may have a diameter greater thanthat of the distal portion 164 and is provided with a plurality offriction elements 168 to allow a user to grasp and turn the lock collar116. The distal portion 164 includes a generally oval-shaped opening 170providing access to the lumen 166. The opening 170 further includes apair of opposing first protrusions 172 and a pair of opposing secondprotrusions 174 located along the inside edge of opening 170. Firstprotrusions 172 are located 180° from one another and are positioned atthe long ends of the oval-shaped opening 170. Second protrusions 174 arepositioned at the narrow sides of the oval-shaped opening 170 (and thusare located at 90° intervals from the first protrusions 172 and 180°from one another). First and second protrusions 172, 174 are eachdimensioned to engage the lateral indentations 150 provided on theengagement tabs 144 of the handle 140, described above.

The interior lumen 166 is dimensioned to receive both of the engagementtabs 144 of the handle 140. Initially, the pedicle access system 110 ofthe present invention may be provided with the locking collar 116attached to the stylet 114 in an initial position. This initial positionis defined by the first protrusions 172 resting in the lateralindentations 150 of the engagement tabs 144 of the handle 140. Uponinsertion of the needle element 142 into the cannula 112, the distalregion 130 of the coupling element 118 of cannula 112 will enter thespace 146 of the handle 140 such that the medial indentations 148 arealigned with (but not yet engaging) the engagement region 131 of thecoupling element 118. At this point, a user would then rotate the lockcollar 116 90° to a second position such that the second protrusions 174rest in the lateral indentations 150. Due to the oval-shaped nature ofthe opening 170, upon rotation of the lock collar 116, the engagementtabs 144 will be forced toward one another, and the medial indentations148 will come in contact with and positively engage the engagementregion 131. As noted previously, this positive engagement prevents thecannula 112 from moving. At the same time, the lock collar 116 serves tolock the engagement tabs 114 in place, effectively locking the cannula112 and the stylet 114 together. The pedicle access system 110 is nowready for use.

FIGS. 31-34 illustrate an example of a pedicle access system 210according to a further alternative embodiment of the present invention.The pedicle access system 210 includes a cannula 212, a stylet 214, alock collar 216 and a retractable insulation sheath 217. As describedabove in relation to pedicle access systems 10 and 110, pedicle accesssystem 210 may be used to percutaneously approach the pedicle, initiatepilot hole formation, and conduct a stimulation signal to the targetsite for the purposes of performing a pedicle integrity assessmentduring formation of the pilot hole. To do this, the cannula 212 andstylet 214 may be lockingly mated and inserted through an operatingcorridor to the pedicle target site, using the handle portion 240 of thestylet 214 to facilitate easy movement and positioning of pedicle accesssystem 210. The pedicle access system 210 may be driven into the bone atthe target site to form a pilot hole while a stimulation signal isapplied and conducted to the target site to assess the integrity of thepedicle during pilot hole formation. The retractable insulation sheath217 functions to ensure maximum efficiency of the stimulation signal asby limiting or preventing shunting of the signal during pilot holeformation. As shown and described herein, the cannula 212, stylet 214and retractable insulation sheath 217 are generally cylindrical inshape. However, it should be understood that cannula 212, stylet 214 andsheath 217 may be provided in any suitable shape having any suitablecross-section (e.g. generally oval or polygonal) without deviating fromthe scope of the present invention.

The retractable insulation sheath 217 functions to ensure maximumefficiency of the stimulation signal as by limiting or preventingshunting of the signal during pilot hole formation. With specificreference to FIGS. 32-34, this is accomplished by providing a tubularinsulation member 274 slideably mated with a housing member 276described in greater detail below. In an initial position (shown inFIGS. 33-34), the tubular insulation member 274 is fully extended suchthat it extends at least to the tip 258 of the stylet 214. Uponformation of a pilot hole in a pedicle (or other piece of bone), thestylet 214 will advance into the bone while the insulation sheathremains outside the bone (a position shown by way of example in FIG.32). Due to the insulative properties of the sheath 217, the electricalcurrent when supplied will be directed into the pilot hole by theuninsulated portion of the cannula 212 and stylet 214 while preventedfrom shunting outside of the hole by the sheath 217.

FIGS. 35-36 illustrate an example of a cannula 212 forming part ofpedicle access system 210 of the present invention. Cannula 212 includesa coupling element 218 and an elongated shaft 220. An interior lumenextends through the cannula 212 from a first opening 222 located at aproximal region 230 of the coupling element 218 to a second opening 224located at a distal end 221 of the elongated shaft 220. Elongated shaft220 may be composed of any conductive material such as metal, forexample. Elongated shaft 220 may include any number of diameter changesincorporated along its length without deviating from the scope of thepresent invention. In the alternative, elongated shaft 220 may beprovided with a uniform diameter along its length.

With reference to FIGS. 37-38, coupling element 218 comprises a proximalregion 230, a center section 232, and a distal portion 234. Proximalregion 230 includes an engagement region 231 dimensioned to engage withthe handle portion 240 of the stylet 214 (as described in further detailbelow). The engagement region 231 may be provided in any suitablegeometric configuration to allow for secure mating with the engagementtabs 144 of the handle 140. By way of example only, the coupling element218 is shown in FIGS. 37-38 having a plurality of triangular-shapedindentations 233, however other shapes are possible. Proximal region 230may include at least one tab member 236 that protrudes in a generallylateral direction from the proximal region 230. By way of example only,as shown in FIG. 38 proximal region 230 includes two tab members 236positioned opposite one another and adjacent to first opening 222. Tabmembers 236 may be utilized to attach supplemental instruments and/orapparatuses to the cannula 212. Center section 232 may be provided witha diameter that is larger than the diameters of the proximal region 230and distal portion 234, and may be provided with a plurality of ridges235 and/or other features for the purpose of providing a suitablegripping area for a user. The distal portion 234 is dimensioned toengage with the elongated shaft 220 of the cannula 212 and may furtherbe provided with a recess 237 for engagement with the sheath attachmentelement 292, described in further detail below.

FIG. 39 illustrates an example of a stylet 214 forming part of thepedicle access system 210. Stylet 214 includes a handle portion 240 anda needle element 242. Referring to FIGS. 41-42, the handle portion 240may (by way of example) resemble a T-handle for providing a user with asuitable gripping means. By way of example only, the handle portion 240may have a substantially hollow interior that is not fully enclosed.Handle portion 240 includes an aperture 243 and a pair of engagementtabs 244 extending distally from handle portion 240. Aperture 243 isdimensioned to allow passage of the needle element 242 from the handleportion 240. Engagement tabs 244 extend generally perpendicularly fromthe handle 240 and generally parallel to one another such that theengagement tabs 244 collectively form an interior space 246. Interiorspace 246 is dimensioned to receive the proximal region 1230 of thecoupling element 218 of the cannula 212. Each engagement tab 244 isprovided with a medial (inwardly-facing) protrusion 248. Medialprotrusions 248 are dimensioned to engage the engagement region 231 ofthe coupling element 218, described above. For this reason, the medialprotrusions 248 may be provided with any geometry complementary to theshape of the engagement region 231 such that when mated, the engagementtabs 244 (via the medial protrusions 248) will prevent movement of theengagement region 231, in effect locking the cannula 212 in placerelative to the stylet 214.

With reference to FIG. 40, the needle element 242 comprises an elongatedshaft 252 having a proximal region 254 and a distal region 256. Theproximal region 254 includes an attachment element 257 configured toattach to the interior of handle portion 240. The attachment element 257is also configured to provide a point of contact for an electricalstimulation source (e.g. a clip attached to an electrical source).Elongated shaft 252 extends distally from proximal region 254 andgenerally perpendicularly from the handle 240 (and through aperture243). Needle element 242 is dimensioned to be inserted through theinterior lumen of cannula 212. The distal region 256 generally includesa distal portion of elongated shaft 252 and a shaped tip 258 having anyform or shape capable of being driven into the pedicle to create a pilothole. By way of example only, shaped tip 258 may have a beveled ordouble diamond form. When needle element 242 is fully inserted intocannula 212, at least a portion of distal region 256 (including shapedtip 258) may protrude slightly from the second opening 224 of cannula212.

Needle element 242 may be composed of any conductive material, such asmetal. Alternatively, needle element 242 may be composed of anon-conductive material with one or more embedded conductive elements ator near the distal end (e.g. distal region 256 and/or shaped tip 258)capable of being communicatively linked with a pedicle integrity testingsystem. Although shown as separate parts, the stylet 214 is preferablyprovided as a single unit, with the needle element 242 and attachmentelement 257 molded in place in the handle 240.

With reference to FIGS. 43-44, a lock collar 216 is provided tolockingly mate the cannula 212 and the stylet 214. Lock collar 216 has agenerally cylindrical overall shape, and includes a proximal portion262, a distal portion 264 and an interior lumen 266 extendingtherethrough. The proximal portion 262 may have a diameter greater thanthat of the distal portion 264 and is provided with a plurality offriction elements 268 to allow a user to grasp and turn the lock collar216. The distal portion 264 includes a generally oval-shaped opening 270providing access to the lumen 266. The opening 270 further includes apair of opposing protrusions 272 located along the inside edge ofopening 270. Protrusions 272 are located 180° from one another and arepositioned approximately midway between the “long ends” and the “narrowsides” of the oval-shaped opening 270. Protrusions 272 are dimensionedto engage the sides of engagement tabs 244 of the handle 240, describedabove.

The interior lumen 266 is dimensioned to receive both of the engagementtabs 244 of the handle 240. Initially, the pedicle access system 210 ofthe present invention may be provided with the locking collar 216attached to the stylet 214 in an initial position. This initial positionis defined by the protrusions 272 resting alongside the engagement tabs244 of the handle 240. The engagement tabs 244 at this point aredisposed in the “long ends” of the oval-shaped opening 270. Uponinsertion of the needle element 242 into the cannula 212, the distalregion 230 of the coupling element 218 of cannula 212 will enter thespace 246 of the handle 240 such that the medial protrusions 248 arealigned with (but not yet engaging) the engagement region 231 of thecoupling element 218. At this point, a user would then rotate the lockcollar 216 90° to a second position such that the protrusions 272 restin against the engagement tabs 244 and the engagement tabs 244 rest inthe “narrow sides” of the oval-shaped opening 270, as shown in FIG. 45.Due to the oval-shaped nature of the opening 270, upon rotation of thelock collar 216, the engagement tabs 244 will be forced toward oneanother, and the medial protrusions 248 will come in contact with andpositively engage the engagement region 231. As noted previously, thispositive engagement prevents the cannula 212 from moving. At the sametime, the lock collar 216 serves to lock the engagement tabs 214 inplace, effectively locking the cannula 212 and the stylet 214 together.The pedicle access system 210 is now ready for use.

According to a further aspect of the present invention, the pedicleaccess system 210 may be provided with a retractable insulation sheath217 to electrically insulate the cannula 212 and stylet 214. Theinsulation sheath 217 may be composed of a non-conductive material orcoated with a non-conductive polymer coating to insulate the sheath 217.This prevents shunting of electrical current during pilot holeformation, increasing the efficiency with which the stimulation currentis delivered to the target area. Referring to FIG. 46, the insulationsheath 217 includes an insulation tube 274 and a housing member 276. Asseen in FIG. 47, the insulation tube comprises a cannulated, elongatedand generally cylindrical member having a proximal end 278 and a distalend 280. The proximal end 278 includes at least one tab 282 configuredto slideably engage the housing member 276 as set forth below. In theexample shown in FIG. 47, the insulation tube 274 includes a pair oftabs 282 positioned opposite one another, however any number of tabs 282may be provided without departing from the scope of the invention. Thedistal end 280 may be provided with a generally tapered surface 284 toallow for an improved interface with the bone.

Referring to FIGS. 46 & 48, the housing member 276 comprises anelongated generally cylindrical member having a proximal end 286, adistal end 287 and an interior lumen 288. The proximal end 286 includesa shaped engagement feature 289 (e.g. a recess as shown) dimensioned toengage a sheath attachment element 292 described in further detailbelow. The housing member 276 further includes at least one elongatedtrack 290 in the form of a cutout section extending substantially thelength of the housing member 276. The track 290 is dimensioned toslideably receive the tabs 282 of the insulation tube 274 such that theinsulation tube 274 is allowed to migrate within the lumen 288.

With reference to FIGS. 49-50, an example of a sheath attachment element292 is shown. The sheath attachment element 292 may be provided as agenerally cylindrical member having an interior lumen 293. Sheathattachment element 292 is dimensioned to provide a snap-fit engagementwith both the housing member 276 and the coupling element 218 of cannula212. The lumen 293 is provided with a first ridge 294 near a distal endfor secure engagement with recess 289 of the housing member 276.Similarly, the lumen 293 is provided with a second ridge (not shown)near a proximal end for engagement with recess 237 of the couplingelement 218 (FIG. 37). During assembly of the pedicle access system 210,the retractable insulation sheath 217 may be provided with the sheathattachment element 292 mated to the housing member 276. The cannula 212is then inserted into the insulation sheath 217 and sheath attachmentelement 292 will then engage the coupling element 218, thus securelyattaching the insulation sheath 217 to the pedicle access system 210.

In use, the pedicle access system 210 is provided with the insulationtube 274 in a first, fully extended position (e.g. FIG. 33). Theinsulation tube 274 will remain in this position as the pedicle accesssystem 210 is advanced through an operative corridor to a bony targetsite (e.g. a pedicle). Upon initial engagement with the bony structure,the tip 258 of the needle element 242 and the distal end 280 of theinsulation tube 274 may contact the bone at approximately the same time.At this point the user may want to begin monitoring the integrity of thepilot hole formation by using a stimulation signal as described below.As the needle 242 is advanced into the bone, forming a pilot hole, thedistal end 280 remains engaged to the outside surface of the bone. Atthe same time, the proximal end 278 (including tabs 282) of theinsulation tube will advance proximally along the track 290 of thehousing member 276. Due to the insulated nature of insulation tube 274,the portion of needle element 242 and cannula 212 that protrude frominsulation tube 274 effectively constitute a stimulation region 260(FIG. 32). As the needle 242 and cannula 212 are advanced into the bonystructure (and the insulation tube 274 remains on the outside of thebony structure), the stimulation region 260 becomes larger. Uponcompletion of the pilot hold formation, the needle 242 and cannula 212are withdrawn from the bony structure, and the pedicle access system 210may be removed from the operative corridor. A spring (not shown) orother control mechanism may be provided to limit the extent of migrationof the insulation tube 274 and/or provide a means for the insulationtube 274 to bias toward returning to the fully extended position uponremoval of the needle 242 from the pilot hole in the pedicle.

In a significant aspect of the present invention, the pedicle accesssystems 10, 110 and 210 described above may be used in combination withneurophysiology monitoring systems and methods to conduct pedicleintegrity assessments while achieving initial access to the pedicle. Byway of example only, the pedicle access systems 10, 110 and 210 may beused in combination with the system and methods shown and described incommonly owned and co-pending Int'l Patent App. Ser. No. PCT/US02/22247,filed on Jul. 11, 2002, the contents of which are hereby incorporated byreference into this disclosure as set forth herein in its entirety. Withreference to FIG. 51, an example of one such neurophysiology system 300includes a display 301, a control unit 302, a patient module 304, an EMGharness 306, including eight pairs of EMG electrodes 308 and a returnelectrode 310 coupled to the patient module 304, and a host of surgicalaccessories 312, including an electric coupling device 316 capable ofbeing coupled to the patient module 304 via one or more accessory cables314.

The neurophysiology system 300 performs pedicle integrity assessments bydetermining the amount of electrical communication between a stimulationsignal and the adjacent nerve root. To do this, a stimulation signal isapplied to the pilot hole or pedicle screw via one of the surgicalaccessories 312. The EMG electrodes 308, positioned over the appropriatemuscles, measure the EMG responses corresponding to the stimulationsignal. The relationship between the EMG response and the stimulationsignal is then analyzed by the system and the results are conveyed tothe user on the display 301. The basic theory underlying the pedicleintegrity test is that given the insulating character of bone, a higherstimulation current (or current density) is required to evoke an EMGresponse when the stimulation signal is applied to an intact pedicle asopposed to a breached pedicle. Thus, if EMG responses are evoked bystimulation currents (or current densities) lower than a predeterminedsafe level, the surgeon may be alerted that there is a possible breach.The neurophysiology system may be provided with software capable ofcompensating for multiple safe stimulation thresholds based on differentcurrent densities being applied to the pedicle by certain geometries ofdifferent instruments.

The pedicle access systems 10, 110 and 210 described above may becombined to and used in conjunction with the neurophysiology system 300by attaching (not shown) the electric coupling device 314 to (forexample) the uninsulated region 28 of the cannula 12 of pedicle accesssystem 10. The electric coupling device 314 may comprise a number ofpossible embodiments which permit the device to attach and hold asurgical tool (such as the pedicle access system 10) while allowingtransmission of a stimulation signal to the tool. One such electriccoupling device 314 utilizes a spring-loaded plunger to hold thesurgical tool and transmit the stimulation signal. The plunger 318 iscomposed of a conductive material such as metal. A nonconductive housing320 partially encases the plunger rod 318 about its center. Extendingfrom the housing 320 is an end plate 324. An electrical cable 326connects the electric coupling device 314 to neurophysiology system 300.A spring (not shown) is disposed within the housing 320 such that in anatural or “closed” state the plunger 318 is situated in close proximityto the endplate 324. Exerting a compressive force on the spring (such asby pulling the cable 326 while holding the housing 320) causes a gapbetween the end plate 324 and the plunger 318 to widen to an “open”position, thereby allowing insertion of a surgical tool between the endplate 324 and plunger 318. Releasing the cable 326 allows the spring toreturn to a “closed” position, causing the plunger 318 to move laterallyback towards the endplate such that a force is exerted upon the surgicaltool and thereby holds it in place between the endplate 324 and theplunger 318. Thereafter the electrical stimulus may be passed from theneurophysiology system 300 through the cable 326 and plunger 318 to thesurgical tool.

Alternatively, the electrical coupling device may be embodied in theform of a clip 328. The clip 328 is comprised of two prongs hingedlycoupled at a coupling point 330 such that the clip 328 includes anattachment end 332 and a non-attachment end 334. A stimulation electrode336 is disposed on the attachment end 332 and communicates with anelectric cable 326 extending from the non-attachment end 334 to theneurophysiology system 300. In a “closed” position the prong ends at theattachment end 332 touch. Depressing the prongs at the non-attachmentend 334 in a direction towards each other causes a gap to form betweenthe prong ends at the attachment end 332. Positioning the “opened”attachment end 332 over a desired surgical tool (such as the pedicleaccess system 10) and releasing the force on the non-attachment end 334causes the attachment end 332 to pinch tight on the surgical tool andthereby allow the electrical stimulus to pass from neurophysiologysystem, through the stimulation electrode 336, to the surgical tool.

The pedicle access system 10 may thus be used to safely access thepedicle and safely form a pilot hole. To do this, the cannula 12, stylet14, and T-handle 16 are preferably all combined and locked together asdescribed above. Using the T-handle 16 to control the movement andpositioning of the pedicle access system 10, the surgeon may positionthe stimulation point on the desired target site. Next, the electriccoupling device 116 may be attached to the uninsulated region 28 ofcannula 12 and the T-handle 16 may be removed to facilitate the use of atool such as a needle driver. Stimulation signals are delivered to thepedicle access system 10 and emitted from the stimulation region 60 asit is being driven in to the bone, forming the pilot hole. Should theneurophysiology system 300 report a potential breach of the pedicle,pilot hole formation may be halted and any steps deemed to be necessaryby the surgeon, based on his or her professional judgment, may be takento correct the problem. Alternatively, the electric coupling device 316may be attached before positioning the pedicle access system 10, and theneurophysiology system 300 may be employed to monitor the proximity ofany nerves during positioning.

In another significant aspect of the present invention, the pedicleaccess system 10 may be used in conjunction with spinal fixation systemsthat require access to pedicle target sites and need pilot holes,including but not limited to those systems shown and described incommonly owned and co-pending U.S. patent application Ser. No.11/031,506 filed Jan. 6, 2005, and commonly owned and co-pending Int'lPatent App. Ser. No. PCT/US05/032300 filed Sep. 8, 2005. Afterpositioning the pedicle access system 10 on the desired pedicle targetsite and safely forming a pilot hole as described above, the T-handle 16and stylet 14 may be unlocked and removed from the cannula 12, leavingthe cannula 12 positioned in the pilot hole. Guide wires subsequentlyused by the spinal fixation systems may then be safely deployed to thepilot hole through the cannula 12. Once the guide wire is in positionthe cannula 12 may be removed from the target site and the surgeon maycommence use of the surgical fixation system.

While the invention is susceptible to various modification andalternative forms, specific embodiments thereof have been shown by wayof example in the drawings and are herein described in detail. It shouldbe understood, however, that the description herein of specificembodiments is not intended to limit the invention to the particularforms disclosed, but on the contrary, the invention is to cover allmodifications, equivalents, and alternatives falling within the scopeand spirit of the invention as defined herein.

What is claimed is:
 1. A system for use in a medical procedure,comprising: (a) a stylet comprising: (i) an elongated needle elementhaving a proximal region and a distal region, said distal regionincluding a shaped tip dimensioned to advance into a bony structure;(ii) a handle portion, wherein the proximal region of needle element isattached to the interior of the handle portion; and (iii) at least twoengagement tabs extending distally from the handle portion and formingan interior space, and (b) a cannula comprising: (i) an elongated shafthaving a proximate end and a distal end and an interior lumen; and (ii)a coupling element positioned at the proximate end of the elongatedshaft, said coupling element having a proximal region and a distalregion, wherein said coupling element proximal region includes anengagement region, and wherein said coupling element distal regionengages the cannula elongated shaft, and wherein said interior spaceformed by the at least two stylet engagement tabs are dimensioned andconfigured to receive the cannula coupling element engagement region andwherein the cannula coupling engagement region is dimensioned andconfigured to lockingly engage the stylet engagement tabs extending fromthe handle portion of the stylet.
 2. The system of claim Error!Reference source not found., wherein the handle portion is a t-handle.3. The system of claim 1, wherein the stylet engagement tabs extendperpendicularly from the handle portion.
 4. The system of claim 1,wherein the stylet engagement tabs have indentations on an outer surfaceof said engagement tabs.
 5. The system of claim 1, wherein the handleportion is a t-handle and where the stylet engagement tabs extendperpendicularly from the handle portion and have indentations on anouter surface of said engagement tabs.
 6. The system of claim 1, whereinthe coupling element proximal region includes at least one tab memberthat protrudes in a lateral direction.
 7. The system of claim 1, whereinthe coupling element proximal region includes at least two tab memberspositioned opposite to one another and adjacent to an opening in thecoupling element proximal region.
 8. The system of claim 1, wherein thecoupling element further comprises a center section with a diameter thatis larger than a diameter of the distal portion of the coupling element.9. The system of claim 1, further comprising a cylindrical sheathattached to an outer surface of the cannula and moveable relative to thecannula.
 10. A system for use in a medical procedure, comprising: (a) astylet comprising: (i) an elongated needle element having a proximalregion and a distal region, said distal region including a shaped tipdimensioned to advance into a bony structure; (ii) a handle portionconnected to the needle element; and (iii) at least two engagement tabsextending from the handle portion, and (b) a cannula comprising: (i) anelongated shaft having a proximate end and a distal end and an interiorlumen; and (ii) a coupling element positioned at the proximate end ofthe elongated shaft, said coupling element having a proximal region anda distal region, wherein said coupling element proximal region includingan engagement region, and wherein said at least two stylet engagementtabs are dimensioned and configured to receive the cannula couplingelement engagement region to lockingly engage the stylet engagement tabsextending from the handle portion of the stylet.
 11. The system of claimError! Reference source not found.0, wherein the handle portion is at-handle.
 12. The system of claim 10, wherein the stylet engagement tabsextend perpendicularly from the handle portion.
 13. The system of claim10, wherein the stylet engagement tabs have indentations on the outersurface.
 14. The system of claim 10, wherein the handle portion is at-handle and where the stylet engagement tabs extend perpendicularlyfrom the handle portion and have indentations on the outer surface. 15.The system of claim 10, wherein the coupling element proximal regionincludes at least one tab member that protrudes in a generally lateraldirection
 16. The system of claim 10, wherein the coupling elementproximal region includes at least two tab members positioned opposite toone another and adjacent to an opening in the coupling element proximalregion.
 17. The system of claim 15, wherein the coupling elementproximal region includes at least two tab members positioned opposite toone another and adjacent to an opening in the coupling element proximalregion.
 18. The system of claim 17, wherein the coupling element furthercomprises a center section with a diameter that is larger than adiameter of the distal portion of the coupling element.
 19. The systemof claim 18, further comprising a cylindrical sheath attached to anouter surface of the cannula and moveable relative to the cannula.
 20. Asystem for use in a medical procedure, comprising: (a) a styletcomprising: (i) an elongated needle element having a proximal region anda distal region, said distal region including a shaped tip dimensionedto advance into a bony structure; (ii) a t-shaped handle portion,wherein the proximal region of needle element is attached to theinterior of the handle portion; and (iii) at least two engagement tabsextending distally and perpendicularly from the handle portion andforming an interior space, said stylet engagement tabs each having anindentation on an outer surface of said engagement tab, and (b) acannula comprising: (i) an elongated shaft having a proximate end and adistal end and an interior lumen; and (ii) a coupling element positionedat the proximate end of the elongated shaft, said coupling elementhaving a proximal region, center region, and a distal region, saidcoupling element proximal region including at least two tab memberspositioned opposite to one another and adjacent to an opening in thecoupling element proximal region, and said coupling element centerregion having a diameter larger than a diameter of the coupling elementdistal region, wherein said coupling element proximal region includes anengagement region, and wherein said coupling element distal regionengages the cannula elongated shaft, and wherein said interior spaceformed by the at least two stylet engagement tabs are dimensioned andconfigured to receive the cannula coupling element engagement region andwherein the cannula coupling engagement region is dimensioned andconfigured to lockingly engage the stylet engagement tabs extending fromthe handle portion of the stylet.